In the case of products in containers, e.g., liquids in bottles or a powdered product in a can, several features are of interest. In the case of liquids in bottles, methods are known for measuring the fill level or the internal pressure. The fill level can be measured directly by means of a broad light beam and a plurality of optical sensors arranged vertically staggered. In addition there are also indirect measurement methods, e.g., by means of the absorption of X-rays or gamma rays or by means of the damping of a high-frequency oscillating circuit. When measuring the fill level by means of X-rays or gamma rays a measuring bridge, which has a radiator on one side of an opening and a radiation detector on the opposite side of the opening, is arranged on the path of the containers such that the nominal fill level lies approximately in the centre of the beam diameter. The beam can for example have a width of 2 cm. The extent of the absorption of the X-ray or gamma ray depends on the fill level as, with a higher fill level a greater proportion of the beam cross-section is absorbed by the product in the container, e.g., the liquid in the bottle. Thus, the lower the fill level the higher the beam output measured by the detector.
A substantial disturbance variable during this measurement arises because the absorption of the X-radiation depends substantially on the atomic weight of the elements contained in the molecules of the product. As a result, two different products show different absorption rates with the same fill level under otherwise identical conditions (same container, same temp. etc.). For example Diet Cola and classic Cola show a difference of approximately four percent in the absorption rate, which means that different threshold values must be entered in order to determine the fill level in order to obtain a uniform result.
In the case of the high-frequency measurement method, the damping due to the fill level is measured by means of a high-frequency oscillating circuit. The fill level substantially changes the capacitive part of the oscillating circuit, i.e., conductivity or dielectric constant and loss resistance, as properties of the contents or product greatly influence the measurement result alongside the fill level. Here too in the case of different products, e.g., two mineral waters with different salt contents, different threshold values must be entered to obtain an equivalent fill-level result.
A further method for determining the fill level of liquids in bottles is described in WO 98/21557, wherein here the result obtained depends on the pressure inside the bottle.
It is known from WO 99/56094 to ascertain the fill level of containers by generating mechanical oscillations in the container wall, by pulse-like deflection of the latter, and then analyzing the oscillations, wherein the decay time, the frequency, the intensity and/or the integral of the intensity or the site of the maximum intensity are recorded.
A further method for determining the fill level in containers is known from WO 99/01722, wherein here the fill level is determined by means of the heat radiation from the container.
The mass of a filled container can also be ascertained in another way, directly by weighing the container or indirectly by measuring the absorption of X-rays taking into account the capacity of the container.
The integrity of products is usually tested by means of chemical analyses. The integrity of the product, in particular of foods, can be destroyed unintentionally by errors in the production process or intentionally or maliciously.